a wrote in news:4723accd$1_2@mk-nntp-
2.news.uk.tiscali.com:

I'm looking at making a parabolic reflector for a wifi link.

I'm trying to work out the distance required between the radiating
element and the reflector.
Should it be an odd number of quarter wavelengths, or an even number?

It is a little different to that, the feed would normally be placed at the
focus of the parabola so that rays emanating from the feed travel to the
reflector, and are reflected in a parallel beam.

For optimal results, the feed should illuminate only the reflector, and the
illumination should be such that the reflected waves have a constant power
density over the projected area of the reflector.

Owen